Ordered porous carbons from hydrothermally treated biomass: Effects of the thermal treatments on the structure and porosity

Abstract

Nitrogen-containing porous carbonaceous materials based on chitosan were successfully prepared by hydrothermal carbonization (HTC) followed by thermal treatments at different temperatures. A detailed characterization of structure, porosity, and chemical composition of these carbonaceous materials was done by X-ray diffraction, scanning electron microscope, thermogravimetric analysis, Raman and infrared spectroscopies, nitrogen adsorption-desorption isotherms, and CHN elemental analysis techniques. Low structural order like amorphous carbons, low porosity, and various functional groups were observed for the precursor hydrochar (obtained from hydrothermal carbonization of chitosan). When this precursor was thermally treated from 200 to 800 °C it was possible to understand its structural transformations due to the changes in the vibrational properties. These results indicate that an increase in the temperature of the thermal treatment promotes an increase in the graphitization degree of the carbonaceous materials. However, it leads to the formation of a defective graphitic-type structure. Furthermore, it was observed an increase in the meso- and micropores up to 600 °C, affecting considerably the porosity and, consequently, the specific surface area of these materials. However, this porous structure can collapse when the treatment temperature increases to 700 and 800 °C. Also, the prepared carbonaceous materials showed high nitrogen content for all temperature interval, and the morphology of the particles was not strongly affected. Our results suggest that thermal treatments of hydrochars are suitable to prepare carbonaceous materials with controlled compositional, structural and textural properties and containing a high nitrogen content.